The trail of blood leads back to those responsible. Any regime or leader that tolerates such killing of innocents has lost its fundamental humanity. Today's news reports of another massacre in Al Kubeir and Kafr Zeta are shocking and sickening. A village apparently surrounded by Syrian forces ... the bodies of innocent civilians lying there ... they were shot ... some allegedly burned or slashed with knives. We condemn this unspeakable barbarity and renew our determination to bring those responsible to account.

His message could not be more urgent, as lives are lost nearly each day -- including an unthinkable number of children -- and countless more are at stake. And as the UN Security Council weighs its next steps, we must keep in mind that any action will be made possible only because United Nations observers are present on the ground. From Houla to Homes to Mazraat al-Qubair, it is their impartial presence that has shone a needed light on atrocities and that enables member states to choose to take decisive action today and in the future.

The UN monitors in Syria are a small, unarmed group of approximately 300 who have been charged with a very large task. They are documenting an accurate account of fatal violence. And while more action remains necessary, they are accomplishing exactly what the global community has asked of them thus far -- providing fact-based reports of the developments in Syria so that member states may respond. They are also doing it at great risk to their own lives, as just this week shots were fired at observers.

And indeed, many UN member states are responding: Last Friday, the Human Rights Council called for an investigation into the killings of 108 civilians in Houla -- the evidence of which could be used in future criminal prosecutions. This followed a move just one day before in which 223 detainees were released in the presence of UN observers -- a simple but important action in something that Annan and UN Secretary-General Ban Ki-moon have called for repeatedly.

Further, observers' reports directly resulted in the expulsion of Syrian ambassadors from nearly a dozen nations last week, including the United States, showing a growing refusal to tolerate the Syrian government's outrageous actions.

All of this follows a February report from the Human Rights Council's authorized investigative team, which detailed evidence that specific individuals within the Syrian regime had ordered their subordinates to engage in "crimes against humanity." These individuals could eventually be referred to the International Criminal Court and prosecuted by the international community for their crimes.

Without the UN presence in Syria, we would lack the clarity and authority to attribute such appalling attacks to the Syrian government and its supporting militias. While it is not observers' mandate to enforce a cessation of violence or compel the Syrian government to adhere to their commitments -- at least not yet -- observers are providing the foundation for the UN Security Council to move forward.

Further, while international humanitarian relief agencies have been consistently denied access to those areas most affected by violence, UN teams are working to bring thousands of Syrian refugees relief in Turkey, Lebanon, and Jordan. The UN Refugee Agency is each day working to provide food, hygiene kits, mattresses, blankets, and other essentials to civilians who have fled Syria.

Still, there are many who say the world must do more. Indeed, the UN can do more to intervene -- but only with the cooperation of Member States and all five permanent members of the Security Council. As Annan said yesterday:

For the sake of the people of Syria who are living through this nightmare, the international community must come together and act as one.

To date, China and Russia, which both wield veto power, have blocked resolutions calling for tougher action on Syrian President Bashar al-Assad. Though the death toll has consistently grown since revolt began in March of last year, these two nations have yet to fully come to the table to begin the process of ending the cycle of violence.

There is likely a long road ahead before we can truly enable Syria's political transition, and until then, innocent lives cry out for the global community to collectively speak out against a regime lacking in fundamental human rights. The ability to maintain objective eyes and ears on the ground has been essential to moving the needle of diplomatic pressure on Syria thus far -- down to and including investigations ordered by the Human Rights Council and the expulsion of Syrian diplomats worldwide.

The work of these UN observers in Syria remains essential, and it signals a call to the world that the time for action is now.